JP3564757B2 - Battery voltage detection device for photographing equipment - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a battery voltage detecting device of a photographing device, and more particularly to a battery voltage detecting device of a photographing device suitable for use in a battery voltage detecting device of a camera.
[0002]
[Prior art]
A battery voltage detecting device of a conventional photographing device will be described by taking a camera as an example.
2. Description of the Related Art In recent years, electronic cameras have become increasingly multifunctional.
The battery built into the camera is gradually consumed by various controls and operations such as auto focus (hereinafter, referred to as AF), automatic exposure (hereinafter, referred to as AE), strobe light emission and display of shooting information in a viewfinder, and the battery voltage is gradually reduced. descend.
[0003]
Specifically, the battery of the camera is used as a common power source for an AF drive motor, a shutter drive magnet, a mirror drive motor, a built-in flash charging circuit, an LED drive circuit for a liquid crystal backlight in a viewfinder, and the like.
The battery of the camera is also used as a power source for ICs such as a microcomputer, a sensor, and a motor driver for controlling the above-described motor and circuit.
[0004]
In the power supply of the above-described IC, the voltage of the battery is set to 5 V or 12 V by a DC-DC converter.
When the battery of the camera is consumed and the voltage of the battery decreases, the output voltage of the DC-DC converter also decreases, and the above-described IC does not operate normally, and abnormalities occur in control of AF and AE.
[0005]
In order to avoid such abnormalities, the battery voltage is detected at regular time intervals during a predetermined time (for example, 8 seconds) after the release switch is half-pressed, and it is determined whether the camera can shoot. Was.
Further, the above-described detection of the battery voltage is not performed during the AF operation in which the battery voltage temporarily decreases, or during the charging of the built-in flash.
[0006]
[Problems to be solved by the invention]
However, as described above, the battery is used for various purposes, and the voltage of the battery fluctuates under the influence of fluctuations in the operation of the circuit. There was a problem that the battery voltage could not be detected accurately.
[0007]
Specifically, there is a method based on PWM control for setting a ratio between ON and OFF of a liquid crystal backlight LED in a finder.
When turning on and off the LED for the liquid crystal backlight by PWM control, the current flowing through the LED greatly changes between ON and OFF.
The voltage of the battery fluctuates under the influence of this change.
[0008]
FIG. 4 is a conceptual diagram illustrating a state in which the voltage of the battery fluctuates due to the influence of the PWM control.
In the figure, symbol T ₀ represents the period for varying the voltage of the battery 1 when the PWM control.
For example, the measurement value is the measurement value m ₂₁ at the time of the measurement value m ₁₁ and a2 at the time of a1 is greatly different.
[0009]
In addition, there is also a problem that if the influence of the PWM control for setting the ON / OFF ratio of the LED for the liquid crystal backlight described above is removed by a filter circuit or the like, the cost increases.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a battery voltage detecting device of a photographing device capable of accurately detecting a battery voltage without increasing costs.
[0010]
[Means for Solving the Problems]
In order to solve the above problem, the battery voltage detecting device of the photographing apparatus according to claim 1 will be described with reference to FIGS. 1 and 2 showing an embodiment. A circuit (9) for generating a periodic fluctuation signal; and a battery voltage detection for measuring the voltage of the battery (1) a plurality of times within a predetermined time and detecting the voltage of the battery (1) based on the plurality of measurements. A circuit (3), wherein the battery voltage detection circuit (3) adjusts the predetermined time for measuring the voltage of the battery (1) to the periodicity (T ₀ ), and performs the measurement of the plurality of times. Each interval is made substantially equal within the predetermined time.
[0011]
3. The battery voltage detecting device according to claim 2, wherein the circuit that generates the periodic fluctuation signal is a circuit that performs PWM control, and the periodic signal is the circuit that is controlled by the PWM control. This is a fluctuation signal generated from.
According to a third aspect of the present invention, there is provided a battery voltage detecting device of the photographing apparatus, wherein the circuit for controlling the PWM controls a LED for a liquid crystal backlight for displaying photographing information.
[0012]
[Action]
The battery voltage detection device of the photographing device according to claim 1, wherein the battery voltage detection circuit adjusts the predetermined time for measuring the voltage of the battery to the periodicity, and sets each interval of the plurality of measurements to the predetermined time. The voltage of the battery (1) can be accurately measured because the voltage is almost equal in the battery.
[0013]
Since the battery voltage detecting device of the photographing device according to the second and third aspects measures the voltage of the battery (1) in accordance with the periodic fluctuation signal by the PWM control, the voltage of the battery (1) is accurately measured. Can be measured.
[0014]
【Example】
FIG. 1 is a schematic diagram of a camera battery voltage detecting device according to an embodiment of the present invention.
In FIG. 1, a battery 1 is a main power supply for operating the camera, and in this embodiment, is composed of two lithium batteries CR123A.
The voltage dividing circuit 2 is a circuit for generating a voltage proportional to the battery voltage of the output of the battery 1. When the input voltage dynamic range of the subsequent circuit is smaller than the maximum output voltage of the battery 1 (about 6V of the open-circuit voltage). Used for
[0015]
In this embodiment, the proportional constant 1 / K of the voltage dividing circuit 2 is set to 5/6 in order to set the dynamic range of the MCU 3 described later to 5V.
The MCU 3 includes an A / D converter 4, a storage unit 5, a calculation unit 6, a determination unit 7, a timer 8, a PWM control unit 9, and a CPU 10.
The A / D converter 4 converts a battery proportional voltage of an analog signal output from the voltage dividing circuit 2 into a digital signal.
[0016]
The storage unit 5 stores a digital signal output from the A / D converter 4.
The calculation unit 6 receives the digital signal stored in the storage unit 5 and performs an average calculation to calculate the battery voltage of the battery 1.
The determination unit 7 compares the battery voltage, which is the calculation result of the calculation unit 6, with a preset reference value, and determines whether or not the current battery voltage of the battery 1 does not hinder shooting by the camera.
[0017]
The determination result of the determination unit 7 is displayed on a liquid crystal display element 11 described later.
The timer 8 supplies an A / D conversion start signal to the A / D converter 4.
The PWM control unit 9 performs PWM control of an LED (to be described later), which is a backlight of a liquid crystal in a viewfinder (not shown).
The CPU 10 controls the storage units 5 to the PWM control unit 9.
[0018]
The liquid crystal display element 11 performs the following three displays on the battery 1 in response to a command from the MCU 3.
That is, the liquid crystal display element 11 performs, as a first display, an indication that shooting is possible when the battery voltage of the battery 1 is sufficient for shooting by the camera.
The liquid crystal display element 11 performs, as a second display, an indication that preparation for replacement of the battery 1 is necessary when the battery voltage of the battery 1 is barely enough for photographing by the camera.
[0019]
The liquid crystal display element 11 performs, as a third display, an indication that shooting is not possible (or the battery 1 needs to be replaced) when the battery voltage of the battery 1 is insufficient for shooting by the camera.
The LED 12 is a backlight of a liquid crystal in a viewfinder (not shown), and uses the battery 1 as a power supply.
[0020]
The battery 1 also supplies power to an AF motor (not shown) and a built-in flash.
The other configuration is the same as that of a known camera, so that the description thereof will be omitted, and the operation of the present embodiment will be described below.
FIG. 2 is a diagram showing a measurement example of the voltage of the battery 1, and FIG. 3 is a diagram showing a flowchart of the CPU 10.
[0021]
Hereinafter, description will be made with reference to FIGS.
In FIG. 2, a symbol T ₀ indicates a cycle in which the voltage of the battery 1 fluctuates when the LED 12 is PWM-controlled by the PWM control unit 9.
Here, BAT _DC indicates the voltage that should be detected.
As shown in the figure, the voltage of the battery 1 fluctuates under the influence of the PWM control.
[0022]
The symbol T1 is an interval at which the voltage of the battery ₁ is measured.
Symbols A1, B1, C1, D1 corresponds to first shows the measurement point in time of the voltage measurement of the battery 1, the time obtained by equally divided into four periods represented by the symbol T _0. That is, in this embodiment, the average value of the four measurements is used as the voltage measurement value.
[0023]
Symbol _M 11 _{~M 14} is a measurement point corresponding to the measurement point. Symbols M ₁₅ is not actually measured, because it equally divided into four periods represented by the symbol T _0, a convenience noted measurement points.
Similarly, the symbol A2, B2, C2, D2 indicates a measurement point in the second time voltage measurement of the battery 1, the symbol _M 21 _{~M 24} is a measurement point corresponding to the measurement point.
[0024]
In the present embodiment, the cycle represented by the symbol T ₀ is set to 256 μSEC, which means that the PWM control pulse output from the PWM control unit 9 has a duty of 100%.
Therefore, four measurements are performed for each 64 μSEC obtained by dividing the 256 μSEC into four parts.
When the release switch (not shown) is half-pressed, the CPU 10 executes the flowchart of FIG.
[0025]
When this flowchart is being executed, the AF motor and the built-in flash (not shown) are not operating.
The CPU 10 performs an initial setting (step 101).
As an initial setting, the CPU 10 sets a variable n representing the number of measurements to one.
CPU10 is to perform the counting of 64μSEC _(T 0/4) in the timer 8 (step 102).
[0026]
Next, the CPU 10 instructs the A / D converter 4 to A / D convert the output of the voltage dividing circuit 2 via the timer 8 (step 103).
The CPU 10 instructs the storage unit 5 to store the A / D converted digital signal (step 104).
The CPU 10 stores the voltage value of the battery 1 at the time point of the symbol A1 in FIG.
[0027]
The CPU 10 determines whether the variable n is 4, that is, whether the measurement has been performed four times (step 105).
At present, since only one measurement has been completed (only the voltage measurement of the battery 1 at the time A1 has been completed), the CPU 10 determines NO and proceeds to step 106.
The CPU 10 increments the variable n by 1 (step 106).
[0028]
The CPU 10 determines whether or not the time measurement by the timer 8 has been completed (step 107).
If the time measurement by the timer 8 has been completed, the CPU 10 returns to step 102, and if the time measurement by the timer 8 has not been completed, the CPU 10 repeats the determination at step 107.
The CPU 10 repeats the loop from step 102 to step 107 until the variable n becomes 4.
[0029]
When the variable n becomes 4, the CPU 10 causes the calculation unit 6 to calculate the average value of the voltage measurement results of the battery 1 one to four times (A1 to D1) (step 108).
The CPU 10 causes the determination unit 7 to determine the calculation result of the calculation unit 6 and causes the result to be displayed on the liquid crystal display element 11 (step 109).
CPU10, as long as the release switch (not shown) is pressed halfway, repeats step 101 to step 109 at measurement intervals of symbols _{T 1.}
[0030]
As described above, according to the present embodiment, the voltage of the battery 1 is measured using the PWM control in which the voltage BAT _DC to be originally detected is varied. The voltage of the battery 1 can be accurately measured without removing the voltage fluctuation.
In this embodiment, the measurement interval of the symbols T ₁ are to good to set to an integral multiple of the symbol T _0, good not be an integer multiple.
[0031]
When the measurement interval of the symbols _{T 1} to an integer multiple of the symbol _{T 0} is matched with the phase corresponding to the phase and A2, B2, C2, D2 corresponding to the symbols A1, B1, C1, D1 shown in FIG. 2 Measurement can always be performed in the same phase.
If not the measurement interval of the symbols _{T 1} to an integer multiple of the symbol _{T 0} is different from the phase corresponding to the phase and A2, B2, C2, D2 corresponding to the symbols A1, B1, C1, D1 shown in FIG. 2 and would, but for averaging a plurality of measurement points (four in this embodiment), negligible influence of errors due to the phase difference of.
[0032]
Further, in the present embodiment, the arithmetic unit 6 is made to perform the average operation. However, it is needless to say that the square root may be used.
[0033]
【The invention's effect】
As described above, in the battery voltage detecting device of the photographing device according to claim 1, the battery voltage detecting circuit adjusts a predetermined time for measuring the voltage of the battery in a periodic manner, and performs each of the plurality of measurements. Since the intervals are made substantially uniform within a predetermined time, the voltage of the battery can be accurately measured with a simple configuration.
[0034]
The battery voltage detecting device of the photographing device according to claim 2 or 3 measures the battery voltage in accordance with the periodic fluctuation signal by the PWM control, and thus removes the periodic fluctuation signal by the PWM control. It is possible to measure the voltage of the battery accurately without the necessity of performing.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a camera battery voltage detecting device according to an embodiment of the present invention.
FIG. 2 is a diagram showing a measurement example of a voltage of a battery 1;
FIG. 3 is a view showing a flowchart of a CPU 10;
FIG. 4 is a diagram showing a change in voltage of a battery 1;
[Explanation of symbols]
1 Battery 3 MCU
4 A / D converter 6 Operation unit 8 Timer 9 PWM control unit 10 CPU
12 LED

Claims (3)

A circuit that uses a battery as a drive source and generates a periodic fluctuation signal;
A battery voltage detection circuit that measures the voltage of the battery a plurality of times within a predetermined time and detects the voltage of the battery based on the plurality of measurements,
The battery voltage detection circuit is characterized in that the predetermined time for measuring the voltage of the battery is adjusted to the periodicity, and that the intervals of the plurality of measurements are made substantially equal within the predetermined time. Battery voltage detector for the device. The battery voltage detection device for an imaging device according to claim 1,
The circuit is a circuit that performs PWM control;
The battery voltage detecting device of the photographing apparatus, wherein the periodic signal is a fluctuation signal generated from the circuit by the PWM control. The battery voltage detecting device of the photographing device according to claim 2,
The battery voltage detecting device of the photographing apparatus, wherein the circuit for performing the PWM control is a circuit for controlling an LED for a liquid crystal backlight for displaying photographing information.

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